Apparatus for treating surfaces



18 6, 1949. H. OSTERBERG APPARATUS FOR TREATING SURFACES 6 Sheets-Sheet 1 Original Filed Dec. 29, 1942 INVENTOR ffl/POAD 0675195586 'BY K ATTOR Y Au 16,1949. H, OSTE'RBER 2,479,541'

APPARATUS FOR TREATING SURFACES Original Filed Dec. 29, 1942 e Sheet-Sheet 2 INVENTOR H/IEOLD OSTE/PEBFG 6, 1949. H. OSTERBERG 2,479,541

APPARATUS FOR TREATING SURFACES Original Filed Dec. 29, 1942 6 Sheets-Sheet 3 INVENTOR f/lffllfi OJTEEBEEG Aug. 16, 1949. HOSTERBERG 2,479,541.

APPARATUS 'FOR TREATING SURFACES I I Original Filed Dec. 29, 1942 a Sheets-Sheet 4 4 KNVENTOR v meow osrf/wfzefi ATTORN Aug. 16, 1949. H. OSTERBERG APPARATUS FOR TREATING SURFACES 6 Shegts-Sheet 5 Original Filed Dec. 29, 1942 Patented Aug. 16, 1949 APPARATUS FOR TREATING SURFACES Harold Osterberg, Buffalo, N. Y., assignor, by

mesne assignments, to American Optical Company, Southbridge, Mass, a voluntary association Original application December 29, 1942, Serial N 0. 470,489. Divided and this application August 30, 1943, Serial No. 500,527

8 Claims.

This invention relates to a new and improved coated article and to new and improved processes and apparatus for producing the same.

This application is a division of my application Serial Number 470,489, filed December 29, 1942.

One of the principal objects of the invention is to provide articles with surface coatings which may be cleaned repeatedly with no substantial damage.

Another object of the invention is to provide a a new and improved method and apparatus for providing more durable and wear resisting reflection reduction coatings to the surfaces of articles.

Another object of the invention is to provide an article having a durable, wear resistant reflection reduction coating thereon.

Another object of the invention is to provide a new and improved method and apparatus for treating or coating the surfaces of light reflecting or transmitting articles so as to substantially reduce the light reflectance thereof and which coatings may be formed as hard and durable as the uncoated surface of such article especially in the case of the softer glasses such as medium flint or barium crown glasses.

Another object of the invention is to provide a light transmitting or light reflecting article having a coating on a surface thereof adapted to substantially reduce the light reflectivity of said surface and which coating may be formed more wear resistant than known prior art coatings.

Another object of the invention is to provide new and improved means and method for va porizing the coating material and increasing the speed of motion of the vaporized particles to provide greater cohesion of the coatings of the articles being coated.

Another object of the invention is to provide a new and improved apparatus for forming coatings of the type set forth.

Another object is to provide means for controlling the direction of motion of the particles and of the coating material to control the deposition of the coating material on the areas desired.

Other objects and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings. It will be understood that the details of construction, arrangement of parts of the apparatus and steps of the process may be changed without departing from the scope of the invention as expressed in the accompanying claims. I therefore, do not wish to be limited to the exact details of construction, arrangement of parts and steps of the process shown and described as the preferred forms have been given by way of illustration only. 1

Referring to the drawings.

Fig. 1 is a sectional View of an apparatus constructed according to my invention;

Fig. 2 is a sectional view showing an article treated according to my invention;

Fig. 3 is a view similar to Fig. 1 but showing another form of apparatus;

Fig. 4 is a top or plan view of one form of crucible member;

Fig. 5 is a side view of the crucible member shown in Fig. 4;

Fig. 6 is a sectional view taken on line 6-6 of Fig. '7 looking in the direction of the arrows;

Fig. 7 is a top or plan view of another form of crucible member;

Fig. 8 is a top or plan view of still another form of crucible member;

Fig. 9 is a sectional view of another crucible arrangement;

Fig. 10 is a sectional view, similar to Fig. 9, but showing another form of crucible arrangement;

Fig. 11 is a top or plan view of the cap member employed by the crucible member shown in Fig. 10;

Fig. 12 is a view similar to Figs. 1 and 3 but showing another form of apparatus;

Fig. 13 is a sectional view of the apparatus shown in Fig. 12 and taken on line I3l3 of Fig. 12 looking in the direction of the arrows; and

Fig. 14 is a view similar to Fig. 12 but showing a further modified form of apparatus.

For some time past there has been considerable interest shown and efiort expended in providing the surfaces of articles with protective coatings and also providing the surfaces of light reflective or light transmitting articles such as optical elements, for example, lenses, prisms, Windows, etc., with coatings which reduce or substantially eliminate the light reflectance of such surfaces and thereby considerably increase the light transmission of said articles.

While such coatings have been successful in substantially reducing or eliminating the light reflectance of the surface of such articles and thereby increasing the light transmission of said articles it has not been possible by prior methods and apparatus for depositing the coating material to form such coatings to obtain coatings having the durability and wear resistance of the uncoated article and it has even been extremely diflicult to make them sufliciently durable and wear resistant to withstand usual handling and cleaning of said surfaces and therefore it was necessary that articles having such coatings on the surfaces thereof be handled delicately to prevent injurythereto. This was particularly so in the -case of opticalinstruments or the like where it was necessary to clean or to remove dust from said coated surfaces and during suchcleaning operation frequently the coating was damaged requiring the removal of said coating and the placing of a new coating on said surface which was both expensive and troublesome.

It is therefore an object of this invention to provide a surface coating which will be substantially permanent and moredurable and .Wear resistant than has been possible in the past.

Referring more particularly to the drawings wherein similar reference characters designate corresponding parts throughout the several views, the apparatus for coating articles according to ?this invention shown in-Fig. 1 comprises the base "I on*'which -ispositioned-the bell jar or .the like 2 to form a vacuum chamber member.

The base I is provided with an opening which is'connected bya pipe 3' to a high vacuum or diffusion pump for evacuating the said vacuum "chamber. Also extending through said base I are two pairs of electrodes] and'5 and .6 and l respectivelyfwhich electrodes are adapted to receive current through the contacts #8, H, 9 and 'lflrespectively to-supply-current within thevacuum chamber as hereinafter described.

'Within the vacuum chamberand in desired location therein is provided the support I2 hav- "ing an opening thereinin which isadjustablypositioned, the supportingmember I3 which sup- "port is adapted to be locked in desired adjusted position by the set screw or the like M.

The supporting'member 13 has the offset'por- .tion l5 formed integral therewith or secured to "the'said 'portionl3 by suitablemeans to support the crucible IS in desired adjusted'position relaitive'to'the heating coil I1.

"Th'e'heating coil "I1 is connected to a current supply through the leads l8 and H! which are secured adjacent their "ends totheir respective electrodesA and 5.

Also on saidbaselis'positioned-the upright support or the like"2ll"having the holdingmem- 'berZl adapted to hold the optical element or fother article tobe coated 22 in position relative to said "crucible so that the lowersurface 23"of "said article22 may'becoated'by vaporized particles which are deposited on the surface '23 'of "saidarticle 22. Over the article His-positioned theheating coil or "heater 24 adapted toreceive "current through'the leads 25 and 26-from the electrodes 6 and 1 respectively and adapted to "heat the articleto be coated in the vacuum prior 'to'the coating thereof or both prior to and after the coatingthereof'as described'in my copend- "ing application, Serial Number 440,778 filed April "28, 1942.

In the crucible support I 6 is placed the insulating'and supporting material [6a for supporting "the crucible 21'on the upper surface'of said in- ?sulating and supporting material 16a and which :material both supports the coating material and "acts as a radiation shield'therefor, therebypre- "venting'heat loss during" the vaporization of said material. Thismaterial l-Ga may be inpowdered tor fused form as described hereinafter or other "suitable material to perform th fun ti set forth above.

The crucible member?! is'preferably formed of carbon or graphite although it may be formed 6 and may be placed directlyon the insulating .may' be placed on said crucible member 21 in finely ground or powdered form or may be prefused into a ball as shown in Fig. 7.

Also the coating may be aluminum or the like where the article to be coated is to form a mirror or reflector.

Below said crucible 21 in the crucible support 16 as shown in Figs. 1 and 3, is placed a quantity of .wan insulating and supporting material I6a. This material may be varied according'to the coating material tobe employed, for example,iif

ithe coating'materiali28 is.to be magnesiumfluoride or quartz then said insulating and supporting material may be of similar material. Or, if the material 28 is magnesiumfluoride then said .insulating andsupportingimaterial may be either magnesium fluoride or quartz or if said coating amaterial 28 is quartz thenrsaidinsulating and :esupporting material may be of quartz or another insulating material of higher melting point than quartz as desired. It isessential that this insulating and supporting material 'have a melt- -ing point which is at least as high as the'melting point of the coating material 28'so that said supporting material will not be markedly disturbed by the heat during the vaporizing of said coating material 28.

It is pointed out that this insulating and supporting material [6a acts -as a support for the crucible21 and also as an insulation and radiationshield therefor.

-As'also shown in Figs. land 3 the'coating material 28 is positioned on or over the crucible *memberi'l. This crucible member may be of various contours and shapes, some of which are shown in Figs. 4 to 11 inclusive.

Figs. 4 and-5 show a strip form cruciblemember WhiIeFigs. 6'and '7 show a circular "crucible member having a depressed central portion 21a adapted to contain the coating material while Fig; 6 shows a circular crucible member having a disk shaped cross "section such'asshown in "Fig. 5.

Fig-9 shows a construction generally similar'to that shown in Figs. 1 and 3 but instead of using the crucible'memberfl'i' as shown insaid Figs. 1

and 3, the coating "material 55 is mixed with carbon or graphite particles'which mixture may be in'powdere'd form or prefused'as shown in'Fig.

or radiationshield body lfi'awhich may be of powdered or fused form as stated above-or said mixture 55 may be placed on any of the formsof crucible shown.

It'is pointedout that this crucible member 21 may be of any other desired contour such as square, oval or other desired contour andalso may be formed of various cross sections but preferably 70 to contain thecoating material.

has adished or depressed'central'portion adapted Also this strip or crucible member "21 is preferably formed of a material adapted toabsorb the heat -=rays such "as graphite or "a carbonaceous material so that the heat radiating from the heating coil [1 is received by the said strip or crucible member 21 which absorbs said heat and conducts or reradiates the same to said coating material 28. The said. coating material 28 may be comprised of magnesium fluoride or quartz or other material as described above or may be comprised of any of said materials having finely ground graphite of carbonaceous material of a high degree of purity fused or mixed therewith so that the heat absorbed by said crucible member 21 will be better conducted or reradiated to said particles of graphite or carbon which are in thermal contact with the coating material and which therefore will readily conduct the heat to said coating material.

In Fig. 10 is shown a further form of crucible member having the cover member 52 which is provided with a series of openings 53 therethrough to allow the vaporized particles to reach the surface of the article to be coated. In this form the coating material 54 may consist of the coating material alone, or be combined with the powdered carbon or graphite and in powdered or prefused form as described above.

In Fig. 3 is shown an arrangement comprising the base I with the bell jar thereon forming a vacuum chamber and containing the crucibles and electrodes previously described in connection with the form of the invention shown in Fig. 1.

The apparatus shown in Fig. 3 differs from that shown in Fig. l, in that in the apparatus of Fig. 3 an arrangement is shown whereby the position of the crucible 21 and crucible support [6 relative to the heating coil I1 may be controlled and varied from without the vacuum chamber and during the operation of the apparatus whereas with the construction shown in Fig. 1, the position of the crucible relative to said heating coil I! may be adjusted only from Within the vacuum chamber and therefore only when the apparatus is not in operation.

In this form the upright 43 supports the curved support or plate 40 which is centered relative to the coating material 28 and which plate is adapted to support the articles or elements 39, the surfaces 44 of which are to be coated and the heating coil 4| is positioned over said support 40 and elements 39 and preferably in substantially concentric relation therewith and the leads 42 and 45 from said heating coil are connected to the electrodes 6 and 1 respectively and are adapted to receive current therefrom.

In the base I is an opening in which is fitted pipe member 32 having the portions 36 and 31 thereof connected with diffusion or other high vacuum pumps to exhaust the vacuum chamber.

Over the upper end of said member 32 which extends into the vacuum chamber is positioned the cover member 39 having the inset portion 3| of rubber or the like adapted to fit over and engage the upper end of said member 32 and seal said opening if desired.

A control rod 35 for said cover 30 has one end connected to said cover member an and has its opposite end extending through the lower end of the exhaust member where there is provided the flexible bellows 38 of a type such as known commercially as Sylphon bellows and said rod 35 has its lower end connected at 46 to an end of the pivoted lever 39 which has a handle for pivotal adjustment of said lever. This lever 39 is pivotally connected at 41 to the plate 49 and has an opening therethrough adapted to be aligned with the arcuate slot 48 in said plate 43 and a bolt is provided through said slot member 48 and spective electrodes 4 and 5.

through said opening in said lever 39 and a wing nut or the like 50 is provided for locking said lever 39 in adjusted relation to said plate 49 to lock said rod 35 and said cap member 33 in adjusted position and thereby lock said crucible support I6 and crucible 21 in adjusted position relative to said heating coil 11. It will be seen that with this construction, that by adjusting the lever 39 as previously described that the cover 39 and crucible support [6 which is positioned on said cover 36 may be raised or lowered to proper position to retain said crucible member and heating coil in said adjusted relation. The cover 30 may be brought into sealing contact with the pipe 32 to permit the bell 2 to be removed without losing the vacuum in the line. With this construction it will also be noted that the relative positions of said heating coil I1 and crucible member 2'! may be varied during the coating operation, thus allowing the adjustment of the crucible member to compensate for any variations in the position of the coating material in the crucible upon the heating of the same.

The apparatus shown in Figs. 12 and 13 is generally similar to the apparatus shown in Fig. 1 in that it contains the base I and bell jar or the like 2 forming the vacuum chamber as well as the upright support 3!] and support member 2| for supporting the article 25 having the surface 23 to be coated.

This apparatus employs three sets or pairs of electrodes, 4 and 5 6 and l and 11 and 18 respectively. The electrodes 4 and 5 have the contacts 8 and II respectively and said electrodes are adapted to supply current to the crucible member 51 which is preferably formed of carbonaceous material such as set forth in my application Serial Number 421,632 filed December 4, 1941 now Patent No. 2,337,679. The said crucible 5! is provided with the integral contact portions 56 and '59 which are connected to the connecting members so and 3! respectively which connecting members are secured to the clamp members 55 and 56 which in turn are connected to their re- The said crucible member 5! is adapted to contain the material of which the coating is to be formed, such as magnesium fluoride, quartz, etc. as described above and to receive current through the electrodes 4 and 5 as previously described to vaporize said coating material by resistance heating.

The electrodes 6 and I, having the contacts 9 and I9 respectively, supply current through the leads 25 and 26 to the heating coil 24 as previously described.

In this form of apparatus an additional pair of electrodes 11 and 18 having the contacts 65 and 66 respectively are provided to supply current through the leads 63 and 64 respectively to the heat coil 62 preferably of tungsten wire. This heating coil both supplies additional heat by radiation to the coating material to assist in vaporizing said material and acts as an accelerator or supercharger, that is, as the vaporized particles of the coating material on rising from the crucible 51 and approach, touch or collide with the wires forming the coil 62 the heat from or temperature of said coil 62 considerably accelerates or increases the speed or velocity of a considerable portion of the particles of coating material thereby causing said articles to hit the surface 23 to be coated with considerably greater force or impact than would be the case without the use of said coil 62. This action tends to cause said particles to adhere more firmly to said sur- :face 23 sandlproducesa verymarked" increase in the adhesion :of the evaporated coat. Moreover it'here i's a tendency whentboiling material in cruci- Jole' fi'lxforihubbles to break and=throvv oii unva- .porized particlesofglobuleswhich are vaporized lin' passinglcoilffil 'This'prevents inarring of the acoated. surface by preventing the depositing of iglobulesrthereon.

Generally, the adhesion of the coating mateirialris in'creased; by increasing the velocity of the revaporated'p'articles or molecules. Inorder that JIHGTCOH fi2lwill increase'the yield of these partiicles orim'olecules, it'is necessary that the temperzatureiofithis coilbe higher than that of the crucible. ilin theevaporation of magnesium fluoride the temperature of the crucible 51 is approxi- Sm'ately .1l'100"C. Since the temperature of the tungsten-icon '62 may be raised to 3100'C., very marked increases in velocity are brought about for thosevaporized particles or molecules which -approachior collide with the coil. Corresponding lincreases'in adhesion oft-he evaporated films or coatings are thenln'oted provided "the vacuum pressure is sufficiently low. Onthe'other hand, we have noted that the adhesion of the evaporated coat is reduced when the coil :62 is maintain'e'd at aitemperature below that of the crucible. The possible increase in velocity of and h'ence adhesion of'the vaporized particles ormol'ecules is greatest for coating substances with low meltin g or boiling points. Thus with lithium 'fiuoride the evaporating temperature is in the neighborhood of 1100 Cxso' that a 2080 C. tell "perature difference can 'be established between thecrucible -51 an'd'the accelerating coil or body The number of particles whose speed is in- 'creasedi's in turn increased by constructing an accelerating coil '62 of tighter windings than -s'hown. The angular distribution of the particles which leave the accelerator coilBZ in the diz'rection of the surface-2E is of importance and may bevari'ed'by'the choice of shape'or -size ofthe'coil 52.

Itis pointed out that coilEiZ is'preferably of such 'sizethat' thebase of the coil is atleast as large as: the crucible containing the coating materialgalthough byreducing the size or area of said 'coil it would be possible to have the speed or velocityofcentral area of the vaporized particles increased'while not'increasing'the speed or velocityof the outer portions ofthe vaporized particles 'andthus the'central area of the coated surface 'may'tbe :made'harder than the outer area thereof.

It is also pointed out that a second coil similar :to the "coil i! may 'bepositi'oned above the-coil l!- in?Eigs.f1"and 3iand'that said second coil wovld :act to incre'ase'the velocity ofthe particles in a :mannersirnilar to COilfiZinFigs. 12"and'14. Also inthe formsshown in Figs. 12 to 14 inclusive a :coil-such'a's i -may-be employed to vaporizethe coating? material by radiated heat' instead of the :resistanceheating in' a crucible "such as shown in thosefigure's.

The above'is a thermal methodfor increasing ithErSDEBd'Of the vaporized particl'esor molecules. Another method that may be employed 'foriincreasing the speed of the vaporized particlesor .molecules is to ionize or electrically charge'these particles and then send'them throughan electricalifieid'.

.The apparatus shown .in Fig. '14 is generally rsimilar-ito :the apparatus of :Figs. .12 and 13 lex- :cept .-that a:modified arrangement for supporting zthearticles- :during the coating :is shown. This arrangement contains a motemfillsadapted to -re- .cei-Vacurren-t athrough the 1eads-68 .and 69. lIhe offset portion ill loft-the motor housin fifl..i .,.piv- =otally-mounted=on an arm--10 which. is connected 5 'totheuprightsupport-Zfl-adjacentthe upper end -0f said ssupport. Thisl allows themotor casing to =be adjusted .tcdesired angularrelation with the source of coating :material in the crucible 51 to controlv thedistributiom of th coating.- material on .10 .the surfaces 16 of theiarticles-tobe coated-as describedin the-.copending applications of Osterberg, Pride-and Luneburg Serial-Number 390,428 :filed April 25,, .1941 now Batent No. 2,35 l ,536 and Serial Number 433 422 :filed March. 5,1942 now :11; Patent No. 2,351,537.

said motor housing. =-is- -adjustably con- ;nectedito the-zsaid arm -ifl-lby means of the Wing nut 12 -twhich-;may be-loosened to allow the angular-.relation ror :said housing :and said source of co =coating material .tonbe varied and then z-said-nut 1:2 is: tightened :to lock Said -members-. inadjusted arelation.

The arm :10 ."is also preferablyrotatably connected to the upright =2 fi to-allowadjustment'of zsaid motorihousing :in a direction at rightangles rtothedirectionof adjustment allowedlby the pivaotal :connection controlledaby'the nut 12. This allows ipractically "universal adjustment :of said .motor housing .and theiarticlesito be coated.

iTheiprotractor or "scale 131s provided to allow setting. .of' saidrhousing lingproper predetermined angular position. a similar. protractor -may be rovided. on the upper-end 0f the upright to allow adjustment :of said housing :in ;predetermined angular position.

Qmthe :end' of-the -shaftl'ld'of the -motor is the ssupportslfiiadapted toisupport thearticleor articles .to The-'coatei'iavvitlrthe surfaces 'lfiitosbe coated incthe'direction-of thez source of coating. material. i Withthis apparatus the;=.article-orarticles'to be coated are rotated by the motor .imprede'ter minediangular relation with the source of coating; matenial'inaorder-to control the distribution -.of.themoatingmaterial. Elfhean'gular position of -i;'-;=aid; support. lfiimaybeldetermined as disclosed in the copendingapplications ireferred :toabove.

:Inmarrying out-the-imethodof this, invention with the apparatus "of Fig. -1, the: :article '22, the surface -fl 3=of whichtisto beicoatedgfirst-has said surface 2 3. which: lSIlOflBGEiVGallhB vaporized coating. material cleaned with-suitable cleaning-solutlons and thenz-saidrarticleds placed-imtheholder 21 Width: its said: surface123= in- .a :direction toward tlresaid cruciblesupportelfi.

In theicrucibieisupportt8] is: placed-the:insulating land supportingimateri-al tea. This material ifiarmay beimagnesium ifluoridelorother material as described (above, depending -.up on. the coating material employed, andathe' crucible member 21 .60 ds then placed therecnand thexcoating-lmaterial s23 isthen" placed; therein or thereover. This-coating material 28 may bemixed-wi-th a :suitable :amount of finely ground-carbon or the-like and ssuclrimixture may: beiplacedtonathe crucible1mem- This carbon imateriali is preferably tin :p'owdered :iorm iwhich is qni-xed with the coating material :cf which the coatingl-is -to be fformed. The prosp'ortions not said .carbonzandsaid :coating 'mate- .701riairmay be Azaried asidesired butI have found ithat .byimixing 140% ofl carboneor agraphitewith -.60-% aofr-Ja coating material' -such asmagnesium fluoride--,that*aicoatingl'having the desired 5 hardness andwearrresistant properties may be fob- 75 taind. il hisr nompositiommay he varied iwithin a very wide range so long as the percentage of graphite or carbon is high enough to absorb considerable heat from the heating coil to facilitate the vaporization of the coating material.

The vacuum chamber is then evacuated by means of the high vacuum or difiusion pumps and forepumps through the opening 3 until the vacuum chamber is evacuated to a desired degree and then current is applied through the electrodes 6 and l to the heating coil 24 to heat the article prior to the coating operation. The article may be then heated in the vacuum to a temperature from 75 degrees centigrade to 300 degrees centigrade for a period of 200 to 20 minutes with the longer heating time using the lower temperatures.

I have found that by heating the article in a vacuum to 200 degrees centigrade for at least 15 minutes to one hour and preferably one hour that when such articles were then coated by the method of this application permanent, wear resistant coatings were obtained. After the article is heated as described above, the current is then applied through the leads 8 and II and electrodes 4 and respectively to the heating coil 1?, the heat from which is radiated to said coating material 28 and crucible or slip member 21 and said crucible member 27 absorbs said heat and conducts the same to said coating material 28. If the finely ground graphite or carbon is mixed with the coating material 28 as described above, then said carbon or graphite particles also absorb said radiated heat from said coil l1 and conduct the same to the coating material.

When the coating material is sufiiciently heated, the particles thereof are vaporized and pass upwards through the coil I1 and are deposited upon the surface 23 of the article 22 and when a coating of sufficient thickness is obtained the current supply to the heating coil I1 is turned oif.

It it preferable that the heating coil 24 be energized during the coating operation and the said coil also may be allowed to heat the article after the coating thereof and the coil I! has been deenergized but this is not absolutely necessary as long as said article is heated prior to the coating operation, as described above.

If the apparatus shown in Fig. 3 is employed the position of the crucible support l5 and coating material 28 relative to said heating coil I 1 may be varied during the coating operation by raising or lowering the lever 39 as previously described. I have found that when the coating is applied by the method and apparatus described above that said coating will be permanent and durable and in fact substantially as durable and wear resistant as un-coated surfaces of articles.

It is pointed out that if desired any of the crucible forms shown in Figs. 4 to 11 inclusive may be employed with any of the forms of apparatus shown.

In using the apparatus shown in Figs. 12, 13 and 14 the vacuum chamber is evacuated and the article to be coated is heated by the heating coil 24 as described above. The current is applied to the crucible 51 and coil 62 as also described above. The heating of the crucible 5T vaporizes the coating material which may or may not be mixed with powdered carbon or graphite and the said vaporized coating material then rises upwardly through the heated coil 62 which increases the speed of said particles as herein before described. In this case the coil 62 also provides additional heat for aiding in vaporizing the coating material.

10 It is particularly pointed out that by preheating the surface to be coated in a vacuum'and then providing the heat conducting means disclosed durable, wear resisting coats will be obtained and that by further providing means for increasing the speed of the vaporized particles, wear resistant coatings can be obtained.

I have found that where the coatings are formed by the process of this application from material such as magnesium fluoride that the resultant coating may be made harder than the inherent hardness of the magnesium fluoride and such coatings may be formed actually harder than many optical glasses such as medium flint or barium crown glasses of which the optical elements may be formed.

Also, it will be seen that by employing the above process of using a proper coating material that a coating may be formed on the surface of an article which coating is in fact harder and more wear resistant than would be the uncoated surface of said article.

In Fig. 2 is shown an article having the coating 29 thereon formed of the coating material in the crucible support l6. I have found that by forming the coating 29 by the apparatus and method herein described that said coating may be formed of a permanent and wear resistant material and substantially as durable and wear resistant as the surface of similar uncoated optical elements.

From the foregoing it will be seen that I have provided simple, efficient and economical means and method for obtainin all of the objects and advantages of the invention.

Having described my invention, I claim:

1. Apparatus for vacuum distillation of coating material comprising a vacuum chamber, means therein for supporting the coating material which is to be distilled, means for supportin an article in position where it is exposed to the vaporized coating material, a source of radiant heat arranged for subjecting the coating material to radiant heat to vaporize said material, and a heat absorbing refractory in heat conducting relation with said material for absorbing radiant heat from said source and conducting it to said material, said refractory being a relatively good absorber of radiant heat.

2. Apparatus for vacuum distillation of coating material according to claim 1 which has heating means for heating the article to be coated.

3. Apparatus for vacuum distillation of coating material comprising a vacuum chamber, means for supporting within said chamber an article which is to be exposed to the vaporized coating material, a refractory container for the coating material, and a source of radiant heat arranged for subjecting said container together with the coating material to radiant heat to vaporize said material, said container being of refractory material which is a relatively good absorber of radiant heat.

4. Apparatus for vacuum distillation of coating material according to claim 3 in which the container for the coating material is supported on a bed of refractory insulating material.

5. Apparatus for vacuum distillation of coating material according to claim 3 in which the relative positions of said refractory container and said heat source may be adjusted to increase or decrease the amount of radiant heat applied to said container and material.

6. Apparatus for coating an article comprising a vacuum chamber, a refractory crucible for eontalning; the. materialused for: coating,, a

. saiicrueiblabeingnflrefractory,materiaL-wl'iih 15 a: relatively; goedabsorbent oiradiantulheat, said crucible having-1 a container portion-inn; re-

ceivingathereon -thewasxtingmatexiali andra eon- -tiguous porticm of:- substantially greater uriace area lthan said .containerspontion. direefilypexposed to. saizl radiant-J heal;- sourcer and. supporting means for. ranlarticle arranged .withinlsaid ban to texposel-saiclearticlel to the vaporized coating material. v

'7. Apparatusufor: 'coatingpan article..accor.ding to claim 6 which includes awbedmoflrlefractompinr rsulating material: for :supperting said crucible.

8. Apparatus for-l lcraating van. article, including :a vacuum chamber, alsunply OfbcQating materiaI therein, and. meansfor. vaporizing saidlcoating material comprisingaa sourcelof ladiantvheatuarlranged for subjecting the sunfacewfi said. coaring. material tolmadianbheartland. meansefm: simultaneouslyr conductingqtomsa idrco ating, material additionall-.heat inaan amount'l sufficientatmraise thmtemperature of the surface oil-said material exposed. 170 said radiant heat; said..las1: named means. including-12aeomminuteda refracizom materiaLin-termixed with theseoating materialsaid refractory, materialhbeing more absorptive rofmadiant-heatlthan .the ooati ngimateria-L OSHIERBERG-l.

REEERENGESZ'GITED;

Tlie" fbllbwing references-are "of" recnrdlnthe filelof this patent? UMTEDESTATES PATENTS;-

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